Naked to the stars

Cal Truent is a dedicated soldier in an interstellar human army, conquering new worlds. During a battle on the third planet from Arcturus, he takes a hit and wakes up with a sixteen-hour hole in his memory.

Haunted by this missing time and facing exclusion from active combat duty due to his superiors' fears of what he might have forgotten, Cal becomes obsessed with recalling those sixteen hours. He joins the Contact Services, a diplomatic unit that handles the aftermath of conquests, a job he previously despised.

Through this experience, he confronts the brutality of Earth's expansionist methods, leading to a profound shift in his worldview and a rejection of the only good alien is a dead one mentality.
Cal journeys toward empathy, show more culminating in a decision to prevent the further destruction of an alien species, the Paumons on Bellatrix, effectively turning against his former military masters. show less

http://nhw.livejournal.com/998040.html

A short book of the proto-military-sf sub-genre, but with rather a subversive message in that context, that the military solution is not enough and a political accommodation is necessary once the conflict is over (if, that is, you actually want the conflict to end). Published in 1961 so the almost-human aliens are either Japanese or Koreans (probably Japanese).